This invention relates to enhanced fish feed and, more particularly, to a method for feeding fish and the enhanced fish feed used during such feeding.
With the reduction in fish stocks worldwide, the raising of aquatic organisms for domestic and international consumption has taken on increased importance. The principal fish species farmed are salmon and trout although other species are also raised, such species including yellowtail, sea bass, perch and the like. Salmon and trout, among others, are carnivorous and rely entirely upon the high protein and energy content of their feed for their growth and health.
Fish are usually raised in fish farms which are situated in open and closed bodies of water including tanks, coastal and freshwater bodies and raceways. The fish farms comprise a plurality of pens, cages or other enclosed areas which constrain the fish and in which the fish are fed and raised. The fish in the enclosures are fed regularly, conveniently by scattering the fish feed on the surface of the water in each of the individual fish enclosures from walkways in a more or less uniform fashion, frequently using a broadcast type feeder or manually by hand. Several techniques exist to determine when to stop feeding, including surface feeding visibility of the feed, pellet sensing devices and monitoring ration size.
When feeding fish without a pellet sensing device, the feeding rate and amount is judged based on surface feeding activities of fish such as splashing and mouthing as viewed by the farmer from the surface. Feeding is stopped or the rate is reduced if pellets are not consumed before they fade into the water column.
Manufactured feeds for farmed fish are normally produced by a process of blending and grinding the ingredients followed by forming the ingredients into pellets. The term xe2x80x9cpelletsxe2x80x9d, however, in this specification as well as the term xe2x80x9cfeedxe2x80x9d is intended to be inclusive of any particle intended to be ingested by fish and variously formulated, including pressed pellets, crumbs, moist feeds, and non-feed particles which may include tablets containing drugs, vaccines, or other substances. The pellets may be coated with fish oil in order to achieve the desired nutritional profile. The feed pellets produced and typically presently used for feeding fish are normally a dark brown color.
There are, however, problems with present fish feeding techniques and with the feed used in such feedings.
Brown pellets are not readily visible from the surface, underwater at depths, under poor water visibility conditions or low lighting conditions. Making pellets more visible (e.g., increasing the contrast of the pellet) will allow farmers to view pellets for a longer period of time as they fade into the water column and therefore offer better control of feed ration and feeding rate. Feeding competition among fish can be reduced and feeding rate can be increased if more fish can see and consume pellets at the same time.
Compared to land animal feeds, salmon and trout feeds are relatively expensive and it is important from a costing and economic point of view that the fish farmer avoid feed wastage by way of overfeeding and underfeeding. In the case of fish reared in sea cages, it is difficult to avoid both over and underfeeding as the conventional dark brown fish feed pellets may not be seen at depth, particularly under conditions of water turbidity, low light conditions such as are present during cloudy days and xe2x80x9cshadingxe2x80x9d in the cages due to the presence of fish.
The siting of fish farms using pens or cages in sheltered locations is also environmentally sensitive. The accumulation of waste feed and fish faeces may lead to nutrient-rich conditions in sediments beneath the fish cages. This can lead to an oxygen imbalance in the area with its concomitant deleterious ecological effects. It is believed that feed waste is normally around 5% or even greater of the feed given. Overfeeding (feeding in excess of the voluntary appetite of fish) wastes feed and pollutes the environment due to feed pellets falling to the sea bed and contributing unwelcome nutrients. This feed wastage also leads to an increase in the amount of feed required per unit weight gain in fish (xe2x80x9cFCRxe2x80x9d). Underfeeding results in lost growth of fish, health problems for fish and, if severe enough, to increased FCR.
Feed ration size varies from meal to meal and from day to day and it is a continuous challenge for fish farmers to know when to stop feeding and the optimum amount of feed to use. Feed tables and surface viewing of the pellet by the farmer or operator while feeding are known to be inadequate techniques and result in a lack of control over ration size. However, these methods are common. Currently, the production of one tonne of salmon or trout requires between 1.1 and 1.3 tonnes or higher of fish feed, and various species of fish, such as the Chinook salmon, may require additional quantities than, for example, the Atlantic salmon. Clearly, the economics of such feeding are of considerable importance to the profitability of fish farms.
In an effort to better control the ration size dispersed during feeding as well as the feeding rate, various pellet sensing devices such as infrared, uplift feedback and underwater cameras have been used with varying success. Underwater cameras have been located in the enclosures generally below the feeding area. When the fish are finished feeding, an increased number of pellets will be observed by the camera dropping through the volume of water where the principal feeding is taking place. When the increase in wasted pellets is observed, the farmer will end the feeding. While this assists the control of ration size, it does nothing to deal with the problems of damage to the fish located in the fish feeding area and the natural reluctance of less aggressive fish to compete for feed.
A number of studies have been published which demonstrate that the color of food items can affect the feed intake of fish. Ginetz and Larkin (xe2x80x9cChoice of colors of food items by rainbow trout (Salmon gairdneri).xe2x80x9d, J.Fish Res.Board Can. 30:229-234) disclosed that the preference of trout for prey of different colors was affected by the background and indicated that salmonids possess keen color discrimination or awareness of contrast between the prey and the background. They further demonstrated that the preference of prey of different colors changed with changing light levels. Against a pale green background, blue food items were preferred in daylight while yellow was preferred at low light levels. Douglas and Djamgoz (xe2x80x9cThe Visual System of Fishxe2x80x9d, Chapman and Hall 1990) taught that the contrast of an object between it and its environment allows for greater detection of the object and this contrast may be a difference of shape, pattern, texture, color or brightness. Browman and Marcotte (xe2x80x9cEffects of prey color and background on feeding by Atlantic salmon alevins.xe2x80x9d Prog.Fish.Cult. 49:140-143 (1987)) disclosed that the background color in aquaria affected choice of prey based on color by fish.
Further difficulties are present using current feeding techniques. First, due to high fish densities which lead to the aforementioned shading in fish cages, there is great competition for the feed among the fish along the surface of the water or in the upper areas directly adjacent the surface where the fish feed is initially distributed. This results in injuries to the feeding fish such as scale loss. This may increase disease and mortality and reduce the quality of the fish. Second, less aggressive fish find that food is unavailable or that there is reduced food available to them during the feeding period, which results in a larger size distribution of the fish. This may reduce fish uniformity which uniformity is desirable for commercial exploitation. Third, since the water darkens as the depth of the water increases, feed may no longer be visible to fish below a certain depth despite being available in sufficient quantities. Fourth, shading is a particular problem with higher fish populations in the cages. This shading reduces the visibility of the feed within the cages in addition to the atmospheric or water turbidity conditions. Because fish, particularly salmon and trout, are primarily visual feeders and rely upon their power of vision to locate feed, these factors take on some considerable importance.
Yet still further problems with existing fish feed are quality control and nutrient content. These problems are heightened as it is desired to have a high energy fish feed with a high fat content. The feed is produced in large quantities using a continuous production process. The fat is added to the dry pellets in a batch mixer that utilizes a vacuum technology to ensure penetration of the oil evenly throughout the pellet filling all the pores in the pellet with fat. As all of the pores become filled with fat and not air as a consequence of the vacuum drawn on the pellet, the incidence of floating feed is reduced. Floating feed is not advantageous since more fish will be concentrated near the surface leading to the aforementioned aggressive and stressful feeding conditions. Likewise, with high energy high fat feed, fat leakage is a problem. Using the aforementioned vacuum technology to ensure even penetration of the fat throughout the pellet helps reduce the amount of fat leakage from the pellets.
Previous techniques in the production of fish feed utilised a continuous coating process. If a quality control problem arose, it was difficult to identify the particular feed exposed to the problem and it was also difficult to achieve the correct amount of fat dose to the pellets. The lack of control of fat dose resulted in working conditions less than optimal and oil spills on production equipment contributed to down time, increased maintenance costs and wastage of fish oil.
According to one aspect of the invention, there is provided an enhanced visibility fish feed for fish ingestion within an enclosure of a fish farm, said enhanced fish feed having significantly improved visibility relative to unenhanced fish feed within said enclosure, said significantly greater visibility being obtained by changing the color and/or reflectivity of said unenhanced fish feed.
According to a further aspect of the invention, there is provided a method of feeding fish within the enclosure of a fish farm with enhanced fish feed having significantly improved visibility relative to the visibility of unenhanced fish feed comprising the steps of selecting said enhanced fish feed and distributing a quantity of said enhanced feed on the surface of the water in said enclosure. fish feed for feeding fish within an enclosure of a fish farm, said fish feed being of a predetermined quantity and having a predetermined contrast with the water conditions within said enclosure.
According to yet a further aspect of the invention, there is provided a method of increasing the fish feeding volume of water below the water surface and within an enclosure of a fish farm, said method comprising determining the depth visibility of fish feed to an operator according to water conditions within said enclosure and correlating said depth visibility to said operator with a known relationship between said depth visibility to said operator and the depth visibility of said feed to fish, and thereafter distributing an enhanced fish feed of appropriate visibility on the surface of said water within said enclosure.